Foot-and-mouth disease (FMD) is one of the most virulent and contagious diseases affecting farm animals. This disease is endemic in numerous countries in the world, especially in Africa, Asia and South America. In addition, epidemic outbreaks can occur periodically. The presence of this disease in a country may have very severe economic consequences resulting from loss of productivity, loss of weight and milk production in infected herds, and from trade embargoes imposed on these countries. The measures taken against this disease consist of strict application of import restrictions, hygiene controls and quarantine, slaughtering sick animals and vaccination programs using inactivated vaccines, either as a preventive measure at the national or regional level, or periodically when an epidemic outbreak occurs.
FMD is characterized by its short incubation period, its highly contagious nature, the formation of ulcers in the mouth and on the feet and sometimes, the death of young animals. FMD affects a number of animal species, in particular cattle, pigs, sheep and goats. The agent responsible for this disease is a ribonucleic acid (RNA) virus belonging to the Aphthovirus genus of the Picornaviridae family (Cooper et al., Intervirology, 1978, 10, 165-180). At present, at least seven types of foot-and-mouth disease virus (FMDV) are known: the European types (A, O and C), the African types (SAT1, SAT2 and SAT3) and an Asiatic type (Asia 1). Numerous sub-types have also been distinguished (Kleid et al. Science (1981), 214, 1125-1129).
FMDV is a naked icosahedral virus of about 25 nm in diameter, containing a single-stranded RNA molecule consisting of about 8500 nucleotides, with a positive polarity. This RNA molecule comprises a single open reading frame (ORF), encoding a single polyprotein containing, inter alia, the capsid precursor also known as protein P1 or P88. The protein P1 is myristylated at its amino-terminal end. During the maturation process, the protein P1 is cleaved by the protease 3C into three proteins known as VP0, VP1 and VP3 (or 1AB, 1D and 1C respectively; Belsham G. J., Progress in Biophysics and Molecular Biology, 1993, 60, 241-261). In the virion, the protein VP0 is then cleaved into two proteins, VP4 and VP2 (or 1A and 1B respectively). The mechanism for the conversion of the proteins VP0 into VP1 and VP3, and for the formation of mature virions is not known. The proteins VP1, VP2 and VP3 have a molecular weight of about 26,000 Da, while the protein VP4 is smaller at about 8,000 Da.
The simple combination of the capsid proteins forms the protomer or 5S molecule, which is the elementary constituent of the FMDV capsid. This protomer is then complexed into a pentamer to form the 12S molecule. The virion results from the encapsidation of a genomic RNA molecule by assembly of twelve 12S pentamers, thus constituting the 146S particles. The viral capsid may also be formed without the presence of an RNA molecule inside it (hereinafter “empty capsid”). The empty capsid is also designated as particle 70S. The formation of empty capsids may occur naturally during viral replication or may be produced artificially by chemical treatment.
Many hypotheses, research routes, and proposals have been developed in an attempt to design effective vaccines against FMD. Currently, the only vaccines on the market comprise inactivated virus. Concerns about safety of the FMDV vaccine exist, as outbreaks of FMD in Europe have been associated with shortcomings in vaccine manufacture (King, A.M. Q. et al, (1981) Nature 293: 479-480). The inactivated vaccines do not confer long-term immunity, thus requiring booster injections given every year, or more often in the event of epidemic outbreaks. In addition, there are risks linked to incomplete inactivation and/or to the escape of virus during the production of inactivated vaccines (King, A.M.Q., ibid). A goal in the art has been to construct conformationally correct immunogens lacking the infective FMDV genome to make effective and safe vaccines.
Vaccinia virus has been used successfully to immunize against smallpox, culminating in the worldwide eradication of smallpox in 1980. Thus, a new role for poxviruses became important, that of a genetically engineered vector for the expression of foreign genes (Panicali and Paoletti, 1982; Paoletti et al., 1984). Genes encoding heterologous antigens have been expressed in vaccinia, often resulting in protective immunity against challenge by the corresponding pathogen (reviewed in Tartaglia et al., 1990). A highly attenuated strain of vaccines, designated MVA, has also been used as a vector for poxvirus-based vaccines. Use of MVA is described in U.S. Pat. No. 5,185,146.
Additional vaccine vector systems involve the use of avipox viruses, which are naturally host-restricted poxviruses. Both fowlpoxvirus (FPV; Taylor et al. 1988a, b) and canarypoxvirus (CPV; Taylor et al., 1991 & 1992) have been engineered to express foreign gene products. Fowlpox virus (FPV) is the prototypic virus of the Avipox genus of the Poxvirus family. The virus causes an economically important disease of poultry that has been well controlled since the 1920's by the use of live attenuated vaccines. Replication of the avipox viruses is limited to avian species (Matthews, 1982) and there are no reports in the literature of avipox virus causing a productive infection in any non-avian species including man. This host restriction provides an inherent safety barrier against transmission of the virus to other species and makes the use of avipox virus based vaccine vectors in veterinary and human applications an attractive proposition.
Other attenuated poxvirus vectors have been prepared by genetic modifications of wild type strains of virus. The NYVAC vector, derived by deletion of specific virulence and host-range genes from the Copenhagen strain of vaccinia (Tartaglia et al., 1992) has proven useful as a recombinant vector in eliciting a protective immune response against an expressed foreign antigen. Another engineered poxvirus vector is ALVAC, derived from canarypox virus (see U.S. Pat. No. 5,756,103). ALVAC does not productively replicate in non-avian hosts, a characteristic thought to improve its safety profile (Taylor et al., 1991 & 1992). ALVAC was deposited under the terms of the Budapest Treaty with the American Type Culture Collection under accession number VR-2547. Yet another engineered poxvirus vector is TROVAC, derived from fowlpox virus (see U.S. Pat. No. 5,766,599).
Recombinant poxviruses can be constructed in two steps known in the art and analogous to the methods for creating synthetic recombinants of poxviruses such as the vaccinia virus and avipox virus described in U.S. Pat. Nos. 4,769,330; 4,722,848; 4,603,112; 5,110,587; 5,174,993; 5,494,807; and 5,505,941, the disclosures of which are incorporated herein by reference. It can thus be appreciated that provision of a FMDV recombinant poxvirus, and of compositions and products therefrom, particularly ALVAC or TROVAC-based FMDV recombinants and compositions and products therefrom, especially such recombinants containing the P1 genes and/or C3 protease gene of FMDV, and compositions and products therefrom, would be a highly desirable advance over the current state of technology.